Various Fungi Colonising Fresh Litter During Winter Inhibit Seed Germination of <i>Picea jezoensis</i>

ABSTRACT Natural regeneration of Picea jezoensis , one of the dominant conifer species in northern Japan, is severely inhibited by soil‐borne pathogens. Although the snow mould Herpotrichia juniperi is known to inhibit seed germination, several studies have suggested the involvement of other pathogens. To clarify the fungal community infecting P. jezoensis seeds under snow, we performed a seed bag experiment and isolated putative pathogens, combined with DNA‐based species identification and inoculation tests. Moreover, metabarcoding analysis was performed to examine the distribution of the isolated species in foliar litter. The experiment was conducted at 12 sites divided between two different altitudes (500 and 700 m) in a natural forest in Hokkaido, Japan. Various species were isolated from ungerminated P. jezoensis seeds; two species, H. juniperi and Neonectria candida , were the most frequently isolated. The isolation rates of these two species differed between altitudes; H. juniperi dominated at higher altitude sites, whereas N. candida dominated at lower altitude sites, with similar or even higher frequencies than H. juniperi . Metabarcoding analysis revealed a high abundance of isolated species, especially H. juniperi , suggesting that fresh litter serves as a reservoir for opportunistic pathogens and negatively affects the natural regeneration of P. jezoensis .